Inspirator assembly



Dec. 31, 1968 R. E. SCHRETER ETAL INSPIRATOH ASSEMBLY Sheet Filed Feb. 8, 1967 INVENTORS ROBERT E. SCHRETER MELVIN J. PARKER syzzrw cuz cgr findusovz ATTORNEYS 1968 R. E. SCHRETER ETAL 3, ,3

INSPIRATOR ASSEMBLY Filed Feb. 8, 1967 Sheet 2 INVENTORS ROBERT E. SCHRETER MELVIN J. PARKER svfim an ATTORNEYS 6 R. E. SCHRETER ETAL 3,419,339

INSPIRATOR ASSEMBLY Filed Feb. 8, 1967 Sheet 3 095 vi i// 4 n /I A 25 m I] INVENTORS l9 ROBERT E. SCHRETER FIG 6 MELVIN a. PARKER ATTORNEYS United States Patent Cfice Patented Dec. 31, 1968 3,419,339 INSPIRATOR ASSEMBLY Robert E. Schreter, Lebanon, and Melvin J. Parker,

Palmyra, Pa., assignors to Hauck Manufacturing Company, Lebanon, Pa., a corporation of New York Filed Feb. 8, 1967, Ser. No. 614,709

12 Claims. (Cl. 431-284) ABSTRACT OF THE DISCLOSURE duct. The Coanda effect causes an efficient entrainment of air into the gas at relatively low pressure and without the need for a blower or other air driving mechanism. The downstream end of the guide member is a parabolic shaped difiuser which prevents the formation of wakes or turbulence which could cause flashback of the flame, and which permits the air-gas mixture to decrease its velocity pressure and attain static pressure regain in a relatively short distance, thus preventing the flame from blowing off.

This invention relates to an inspirator assembly, and more particularly to an improved mixing device for an inspirator assembly for forming an intimate mixture of gases.

In a typical fuel gas-air mixing system for a gas burner assembly, fuel gas is supplied under high pressure to the nozzle of an inspirator which injects the gas into the throat of a venturi at a relatively high velocity. The energy of the gas stream is used to inspirate air into the stream. The inspirator also mixes the air with the gas and delivers the desired mixture to a combustion device. In these systems, the gas must be supplied under relatively high pressure, however, to provide suflicient energy to inspirate the necessary air for combustion and to provide sufficient static pressure to satisfy the needs of the combustion device.

Another type of air-gas mixing system suitable for fuel gases is the low pressure proportional mixer in which gas at atmospheric pressure is inspirated or drawn into a stream of air flowing at relatively low pressures. In such a system, however, a blower, or the like, is required to provide the necessary flow of air to inspirate the required amount of gas.

Both the high and low pressure mixing systems also require a relatively long diverging discharge nozzle which must be of suflicient length to permit the eflicient conversion of velocity into static pressure.

Accordingly, it is the primary object of this invention to provide a new and improved inspirating device.

Another object of this invention is to provide a new and improved inspirating assembly which is physically much smaller than existing inspirating devices.

A further object of this invention is to provide a gasair mixing device for an inspirator assembly which does not require a blower or other air driving mechanism.

Still a further object of this invention is to provide a mixing device for an inspirator assembly that achieves eflicient static pressure regain without requiring a long venturi section.

Still another object of one embodiment of this invention is to provide a gas-air mixing device for entraining combustible amounts of air in flowing stream of gas supplied under relatively low pressure.

Still a further object of one embodiment of this invention is to provide an inspirator assembly that is compact in size, readily attachable to a combustion chamber, burner nozzle, or the like, and is inexpensive to manufacture.

Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention are realized and attained by means of the instrumentalities and combinations as particularly pointed out in the appended claims.

The following discussion of the principles embodied within the gas-air mixing device of this invention will be helpful to a clear understanding of the invention. When a pressurized elastic fluid, such as fuel gas, emerges from an orifice into a surrounding atmosphere of another elastic fluid, such as ambient air, a suction force is cre ated on the ambient air inducing it into the emerging stream of gas. This principle is the basis for operation of the conventional air-gas inspirator assembly in which gas is injected into the throat of a venturi at a relatively high velocity to inspirate air into the gas stream.

If an unbalancing effect is provided on the flow of the ambient air into the emerging gas stream, such as by mounting a lip on one side of the orifice, the gas stream will move toward the side on which the flow of surrounding fiuid has been made more diflicult. This physical phenomenon is known as the Coanda effect and is more fully described in US. Patent No. 2,052,869. Under this eflect it has been found that considerably more of the ambient fluid can be induced into the fluid emerging from the orifice than when no unbalancing effect is provided.

To achieve the Coanda efiect the lip of the orifice should progressively recede away from the direction of emergence of the fluid from the orifice. The lip prevents surrounding fluid from flowing into the space between the lip and the emerging stream of fluid. Thus as the ambient fluid, which is in the space between the lip and the emerging stream, is drawn into the emerging fluid stream, additional ambient fluid cannot fill this space and a partial vacuum is created adjacent the lip. The partial vacuum adjacent the lip creates a suction force on that side of the emerging fluid stream which is adjacent the lip. This suction force deflects or pulls the stream closer to the lip. The deflection of the emerging fluid toward the lip, in turn, increases the suction force on the ambient fluid on the opposite side of the emerging fluid from the lip. This increased suction force induces-significantly more ambient fluid into the emerging fluid than would be drawn into a fluid emerging from an identical orifice having no lip or obstruction.

The inspirator assembly of this invention comprises a housing having an upstream end open to air, a downstream end leading to a burner device, and an air-gas mixing device within said housing. The mixing device includes a duct extending into said housing for supplying gas under pressure, and a guide mounted within said housing and being aligned with and positioned close to the discharge end of the duct. The discharge end of the duct and the guide define a slot for discharging gas from the duct in a substantially radial direction. The surface of the guide adjacent the discharge end of the duct is substantially symmetrical about a central axis of the guide and progressively recedes downstream from the radial direction of emergence of gas through the slot to cause a stream of gas emerging from the slot to be deflected toward the receding surface of the guide and to entrain air, from the housing, into the gas stream.

Preferably, the surface of the guide adjacent to the discharge end of the gas duct is hemispherical. The guide may also include a diffuser section downstream from the hemispherical surface. This diffuser section, which desirably is parabolic in shape, causes the gas-air mixture to decrease its velocity pressure and attain static pressure regain.

Where the inspirator assembly and burner device are to be closely coupled, it is also desirable to provide inwardly converging walls extending downstream from a point near the base of the diffuser to obtain relatively uniform velocities and to avoid the existence of a low forward velocity eddy, which, if carried out through the burner nozzle, would afford an opportunity for the flame in the burner to flash back into the inspirator assembly.

Means may be provided in the inspirator assembly for adjusting the width of the gas slot between the duct and the guide to permit the inspirator to attain maximum efficiency with different types of fuels.

It is to be appreciated that the inspirator assembly may be used with air as the pressure gas and include a liquid fuel atomizer at or near the end of the diffuser to permit the inspirator to operate with a liquid fuel, such as oil.

The accompanying drawings illustrate specific embodiments of the invention, and, together with the description, serve to explain the principles of this invention.

In the drawings:

FIG. 1 is a side elevation, partially in section, of an embodiment of the inspirator assembly of this invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a perspective view of the mixing device of the inspirator assembly of FIG. 1;

FIG. 4 is a schematic illustration of the operation of the inspirator assembly of FIG. 1;

FIG. 5 is a fragmentary side elevation, partially in section, of the downstream end of an embodiment of the inspirator assembly of this invention in combination with a flame-retaining nozzle; and

FIG. 6 is a side elevation, partially in section, of another embodiment of the inspirator assembly of this invention incorporating an auxiliary liquid fuel atomizer.

It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention, the scope of which is defined in the accompanying claims.

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the drawings.

As shown in FIGS. 1-2, the inspirator assembly of this invention includes a housing 10 having an upstream end 12 open to the ambient air and a downstream end 14 leading to a burner device or combustion chamber shown generally at 16. A joint 19 is provided in an opening 18 in the side of housing 10 for connection of the inspirator assembly to a conventional fuel gas supply line.

As shown in FIGS. 1-3, a gas-air mixing device is provided Within housing 10 for entraining air into a gas stream to provide a combustible mixture of fuel gas and air to burner device 16.

The gas-air mixing device includes a gas supply duct generally indicated at 20 having a supply conduit 24 connected to joint 19 and a discharge chamber 22 terminating at an open end 30. Supply duct 20 is suitably secured to the housing as by screws 25 passing through the housing and threadably engaged to an aerodynamically designed supporting plate 26 secured to conduit 24. A gasket 27 is provided between plate 26 and the inside surface of the housing to provide a leakproof connection between joint 19 and conduit 24.

Supply duct 20 has a smooth outer cylindrical surface 28 with a streamlined upstream end 2. l9 minimize resistance to the flow of air entering housing 10 through open end 12.

In accordance with this invention, a guide, generally indicated at 32, is provided in housing 10 for causing the stream of gas to emerge from supply duct 20 in a substantially radial direction and for causing the gas stream to induce air from the housing into the gas stream.

As here embodied, guide 32 is symmetrical about its central axis 33, and is located coaxial with end 30 of discharge chamber 22 of supply duct 20. End 30 of supply duct 20 and the surface of guide 32 define an annular slot 34 through which gas can emerge into housing 10.

Guide 32 includes an entrainment section 36 having a hemispherical surface 38 which progressively recedes away from the direction of emergence of the gas from slot 34, and a diffuser section 40 having a parabolic or cone-shaped surface 41. A rod 42 is provided projecting upstream from the entrainment section of guide 32 and is secured within an opening 44 in supply duct 20 to hold guide 32 in the desired location with respect to the discharge end 30 of supply duct 20.

Rod 42 is threadably engaged by an adjustment screw 46 protruding through upstream end 29 of supply duct 20. Screw 46 permits axial adjustment of guide 32 with respect to supply duct 20 to vary the width of annular slot 34 between the end 30 of supply duct 20 and entrainment section 36 of guide 32. A set screw 48 is further provided to engage rod 42 and lock guide 32 in the desired location.

In the operation of the mixing device of this invention, as schematically illustrated in FIG. 4, gas, indicated by arrows 50, is supplied under pressure through supply duct 20. Gas 50 emerges from annular slot 34 in a radial direction substantially normal to the axis of discharge chamber 22 of supply duct 20.

As gas 50 emerges from slot 34, the stream reduces the local pressure at entrainment section 36 and is deflected toward hemispherical surface 38 of guide 32. This deflection of the gas stream causes ambient air to flow toward surface 38 and to be entrained into the gas stream as indicated by arrows 52.

The receding surface 38 of entrainment section 36 of guide 32 should be long enough to allow a sufficient amount of air to be entrained in the gas stream to provide a completely combustible mixture. The amount of air required will depend upon the requirements of the particular gas being used. The desired entrainment ratio of air to gas must be substantially reached by the time the airgas stream passes over the end of the entrainment section is of the guide 32 and begins to flow along diffuser section When the gas stream flows along hemispherical surface 38 of guide 32 continuously entraining air into the stream, the gas-air mixture layer expands due to the increased amounts of air now flowing with the stream. This expansion is continuous until the gas-air mixture reaches the widest point 68 of entrainment section 36 prior to passing into diffuser section 40 of the inspirator assembly. At this point the gas stream ceases to entrain any more air and begins to slow down to achieve the desired conversion from velocity to static pressure.

A sufficient distance 53, therefore, is provided between the widest point 68 of guide 32 and the inside Wall 66 of housing 10 (see FIG. 4) to permit the gas-air mixture to flow through this area of the burner assembly without obstruction or unnecessary pressure loss.

Diffuser section 40 of guide 32, while not essential to achieving the proper entrainment ratio of air in the gas, is desirable to permit the eflicient transformation of velocity to static pressure and also to assist in providing a uniform gas velocity at the outlet of the inspirator.

If the inspirator assembly is coupled directly to a burner device and the velocity of flow of the gas-air mixture into the burner is too high, the flame in the burner will blow off; and consequently, it is necessary to lower the velocity of the gas-air mixture for close coupled units. If the velocity is too low or if the velocity profile is such that any portion of the mixture stream has a velocity less than the rate of flame propagation of the mixture, then the flame Will flash back into the inspirator. Thus it is desirable to increase the cross-sectional area of the inspirator outlet through which the gas-air mixture flows to decrease the velocity of the mixture to a desired amount. The increase in area, however, should not be so abrupt that turbulence will be created in the mixture stream resulting in conversion losses or low velocity areas in the flow of the mixture stream.

In a conventional inspirator, the divergent section of the venturi is usually quite long in order to provide for etficient conversion of velocity to static pressure. Generally speaking, this long divergent section provides for not only an efficient conversion but also for a relatively uniform velocity across the cross-section of the outlet of the inspirator.

The required decrease in the velocity of the mixture in the present inspirator assembly is provided by the diffuser 40 which progressively increases the cross-sectional area of the chamber 54 through which the mixture flows.

The diffuser also assists in preventing the formation of wakes downstream of the entrainment section 36 of guide 32. Under normal circumstances, if no diffuser were attached to entrainment section 36, a turbulent zone would form in the lea of entrainment section 36. This turbulent, low velocity area would provide a flashback path from the burner into the inspirator assembly. By providing the diffuser section downstream of entrainment section 36, pro vision is made for the transition of the annular stream to a solid stream without excessive turbulence.

Converging walls 58 are provided on the inside of housing to further help stabilize the gas-air mixture so that a smooth flowing stream of relatively uniform velocity is achieved.

A flame holder may be attached to housing 10 to help preserve the flame structure and prevent flashback. As shown in FIG. 5, flame retaining nozzle, generally 60, is mounted at open end 14 of housing 10. An annular flange 61 is mounted internally of nozzle 60 and forms an annular recess 62 adjacent the internal wall of nozzle 60. A plurality of spaced ports 64 connect recess 62 with open end 14 of housing 10. Ports 64 permit a small part of the gas-air mixture from chamber 54 to flow into annular recess 62. The gas-air mixture burns in recess 62, thus assisting in maintaining the primary flame in the burner.

The supply of fuel gas, and in particular natural gas from the utilities, is subject to unexpected interruptions in service and therefore it is often desirable to provide an auxiliary source of fuel to maintain continuous combustion in a furnace, or the like. Conventionally, liquid fuel, such as oil, is used as the auxiliary fuel, and an embodiment of this invention, illustrated in FIG. 6, is capable of advantageously converting from providing a gas-air mixture to providing a liqiud fuel-air mixture.

Referring to FIG. 6, a conventional liquid fuel atomizer 70 is mounted in the tip of diffuser 40 of guide 32. Atomizer 70 is connected to an auxiliary source of liquid fuel through a conduit 72 extending along center line 33 of guide 32, and through shaft 42 which is hollow. Conduit 72 exits through an opening in the side of shaft 42 and a slot 74 in the upstream extension of supply duct 20. In the event of interruption of the supply of fuel gas, air under pressure is supplied to supply duct 20 which entrains additional air in housing 10 in a similar manner to the entrainment of the air in the fuel gas as previously described. As the flow of air passes out of housing 10 and into burner device 16, oil is sprayed through atomizer 70 into the flowing air stream to provide a combustible mixture of oil and air.

Any conventional fuel gas regardless of its thermal quality and its air to gas combustion ratio is suitable for use in the inspirator assembly of this invention. The mixing device is adjustable so that the desired entrainment ratio can be achieved depending upon the particular fuel gas selected. With this inspirator assembly, it is not necessary to supply the gas under as high a pressure as in a conventional high pressure inspirator or to provide blowers or other means to force the air as in a conventional low pressure inspirator.

The inspirator of the present invention has a significantly greater efliciency than a conventional commercial inspirator and thus is capable of attaining the same volume of inspirated air :as a conventional inspirator while utilizing a significantly lower gas inlet pressure.

The lower operating pressure permissible with the present inspirator permits conversion from velocity to static pressure to take place in a relatively short diverging nozzle, thus eliminating the need for a long venturi section to achieve efficient static pressure regain.

The invention in its broader aspects is not limited to the specific details shown and described, but departures may be made from such details within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. An inspirator assembly for providing a mixture of gas and air comprising: a housing having an upstream end open to air and a downstream end open for connection to a burner device; a duct extending into said housing for supplying gas under pressure, said duct having a discharge end; a guide mounted within said housing and being aligned with and positioned close to the discharge end of said duct, the discharge end of said duct and said guide defining a slot for discharging gas from the duct in a substantially radial direction, the surface of said guide adjacent said duct being substantially symmetrical about a central axis of the guide and progressively receding downstream from the radial direction of emergence of gas through the slot to cause a stream of gas emerging from the slot to be deflected toward the receding surface of said guide and to entrain air, from the housing, into the gas stream to form a mixture of gas and air, said guide including a parabolic shaped diffuser coaxial with and having a tapered surface extending downstream from said substantially symmetrical surface of said guide.

2. The inspirator assembly of claim 1, wherein the slot is annular.

3. The inspirator assembly of claim 1, wherein the substantially symmetrical surface of the guide is a spherical surface.

4. The inspirator assembly of claim 3, wherein the spherical surface is a hemisphere.

5. The inspirator assembly of claim 1, including inwardly converging walls on the inside of the housing extending downstream from a point near the base of the diffuser, said converging walls and the surface of the diffuser providing an expanding area in the direction of flow of the mixture.

6. The inspirator assembly of claim 5, including flame retaining means mounted on the housing downstream of Lhe lguide to preserve the flame structure and prevent flash- 7. The inspirator assembly of claim 1, including means for adjusting the width of the slot between the end of the duct and the receding surface of the guide.

8. The inspirator assembly of claim 1, wherein a rod is secured to the guide and is slidably mounted in the supply duct to support the guide.

9. An inspirator assembly providing a mixture of two gases comprising: a housing having an upstream end open to a supply of one gas, a downstream end open for connection to a burner device; and a mixing device within said housing, said mixing device including a duct extending into said housing for supplying another gas under pressure, a guide mounted within said housing and being aligned with and positioned close to the discharge end of said duct, the discharge end of said duct and said guide defining a slot for discharging gas from said duct in a substantially radial direction, said guide having a hemispherical surface extending downstream from the radial direction of emergence of gas through the slot to cause a stream of gas emerging from the slot to be deflected toward the receding surface of said guide and to entrain the gas from said housing into the emerging stream and a parabolic diffuser coaxial with and having a tapered surface extending downstream from said hemisphere.

10. The inspirator assembly of claim 9, including flame retaining means mounted on the housing downstream of the guide to preserve the flame structure and prevent flashback.

11. The inspirator assembly of claim 9, wherein both gases are air and a liquid fuel atomizer is located near the downstream end of the parabolic diffuser to inspirate liquid fuel into the flowing stream of air.

12. The inspirator assembly of claim 11, wherein the liquid fuel atomizer is located in the end of the diffuser.

References Cited UNITED STATES PATENTS 562,089 6/1896 Oakman et al 239417.3 1,697,549 1/1929 Wolff 239-4173 2,860,483 11/ 1958 Fox. 3,215,187 11/1965 Tinker 158--76 3,224,488 12/ 1965 Skonecke et al. 15873 3,227,202 1/1966 Morgan 158-1.5 X 3,319,692 5/1967 Reba et al. 158-1 FOREIGN PATENTS 529,316 11/ 1940 Great Britain.

CHARLES J. MYH-RE, Primary Examiner.

E. G. FAVORS, Assistant Examiner.

US. Cl. X.R. 

